Re: [PATCH 2/2 v5] Fix reverse stepping multiple contiguous PC ranges over the line table.

Simon Marchi via Gdb-patches
2023-06-19T17:58:49Z

On 5/16/23 18:54, Carl Love wrote:
> Bruno, Simon, GDB maintainers:
>
> Version 5, changed comments in test case func-map-to-same-line.c.
> Patch 1/2 implemented the new options for gdb_compile. Updated the
> call to proc run_tests to use the new gdb_compile options in a
> foreach_with_prefix loop.
>
> Version 4, additional fixes for gcc version check, wrap function calls
> using "with_test_prefix", move load_lib dwarf.exe. Fixed typo noted by
> Luis.
>
> Version 3, added the gcc version check as discussed further from
> version 2 of the patch. Also updated the tests to check for supporting
> reverse execution rather than requiring recording. I also noticed
> there were a couple more instances of a requirement check, i.e. if []
> which I changed to "require" per the current style for checking on the
> test requirements.
>
>
> The following patch fixes issues on PowerPC with the reverse-step and
> reverse-next instructions when there are multiple assignment statements
> on the same line and when there are multiple function calls on the same
> line. The commit log below discusses these issues in further depth.
> The discussion included what the correct operation should be for these
> commands based on the GDB documentation. The proposed patch at that
> time changed how the commands worked on other platforms such as X86 in
> a way they no longer matched the documentation.
>
> The issue is the line table contains multiple entries for the same
> source line. The patch adds a function to search the line table to
> find the address of the first instruction of a line. When setup up the
> reverse stepping range, the function is called to make sure the start
> of the range corresponds to the address of the first instruction for
> the line. This approach was used. When Luis initially developed the
> patch, he considered merging the contiguous ranges in the line table
> when reading the line tables. He decided it was better to work with the
> data directly in the line table rather than creating and using a
> modified version of the line table.
>
> The following patch fixes the execution of the reveres-step and
> reverse-next commands for both senarios of multiple statements on the
> same line for PowerPC and aarch64-linux. Unlike the previous patch, it
> does not change the operation of the commands on other platforms, i.e.
> X86. The patch adds new test cases for both scenarios to verify they
> work correctly.
>
> The patch has been tested on PowerPC, Intel X86 and aarch64-linux with
> no new regression failures.
>
> Please let me know if the patch is acceptable for mainline. Thanks.
>
> Carl
>
> ---------------------------------------------
> Fix reverse stepping multiple contiguous PC ranges over the line table.
>
> There are a couple of scenarios where the GDB reverse-step and reverse-next
> commands do not work correctly.
>
> Scenario 1 issue description by Luis Machado:
>
> When running GDB's testsuite on aarch64-linux/Ubuntu 20.04 (also spotted on
> the ppc backend), I noticed some failures in gdb.reverse/solib-precsave.exp
> and gdb.reverse/solib-reverse.exp.
>
> The failure happens around the following code:
>
> 38 b[1] = shr2(17); /* middle part two */
> 40 b[0] = 6; b[1] = 9; /* generic statement, end part two */
> 42 shr1 ("message 1\n"); /* shr1 one */
>
> Normal execution:
>
> - step from line 38 will land on line 40.
> - step from line 40 will land on line 42.
>
> Reverse execution:
> - step from line 42 will land on line 40.
> - step from line 40 will land on line 40.
> - step from line 40 will land on line 38.
>
> The problem here is that line 40 contains two contiguous but distinct
> PC ranges in the line table, like so:
>
> Line 40 - [0x7ec ~ 0x7f4]
> Line 40 - [0x7f4 ~ 0x7fc]
>
> The two distinct ranges are generated because GCC started outputting source
> column information, which GDB doesn't take into account at the moment.
>
> When stepping forward from line 40, we skip both of these ranges and land on
> line 42. When stepping backward from line 42, we stop at the start PC of the
> second (or first, going backwards) range of line 40.
>
> Since we've reached ecs->event_thread->control.step_range_start, we stop
> stepping backwards.
>
> ---------------------------------------------------------
>
> Scenario 2 issue described by Pedro Alves:
>
> The following explanation of the issue was taken from the gdb mailing list
> discussion of the withdrawn patch to change the behavior of the reverse-step
> and reverse-next commands. Specifically, message from Pedro Alves
> <pedro@palves.net> where he demonstrates the issue where you have multiple
> function calls on the same source code line:
>
> https://sourceware.org/pipermail/gdb-patches/2023-January/196110.html
>
> The source line looks like:
>
> func1 (); func2 ();
>
> so stepping backwards over that line should always stop at the first
> instruction of the line, not in the middle. Let's simplify this.
>
> Here's the full source code of my example:
>
> (gdb) list 1
> 1 void func1 ()
> 2 {
> 3 }
> 4
> 5 void func2 ()
> 6 {
> 7 }
> 8
> 9 int main ()
> 10 {
> 11 func1 (); func2 ();
> 12 }
>
> Compiled with:
>
> $ gcc reverse.c -o reverse -g3 -O0
> $ gcc -v
> ...
> gcc version 11.3.0 (Ubuntu 11.3.0-1ubuntu1~22.04)
>
> Now let's debug it with target record, using current gdb git master (f3d8ae90b236),
> without your patch:
>
> $ gdb ~/reverse
> GNU gdb (GDB) 14.0.50.20230124-git
> ...
> Reading symbols from /home/pedro/reverse...
> (gdb) start
> Temporary breakpoint 1 at 0x1147: file reverse.c, line 11.
> Starting program: /home/pedro/reverse
> [Thread debugging using libthread_db enabled]
> Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
>
> Temporary breakpoint 1, main () at reverse.c:11
> 11 func1 (); func2 ();
> (gdb) record
>
> (gdb) disassemble /s
> Dump of assembler code for function main:
> reverse.c:
> 10 {
> 0x000055555555513f <+0>: endbr64
> 0x0000555555555143 <+4>: push %rbp
> 0x0000555555555144 <+5>: mov %rsp,%rbp
>
> 11 func1 (); func2 ();
> => 0x0000555555555147 <+8>: mov $0x0,%eax
> 0x000055555555514c <+13>: call 0x555555555129 <func1>
> 0x0000555555555151 <+18>: mov $0x0,%eax
> 0x0000555555555156 <+23>: call 0x555555555134 <func2>
> 0x000055555555515b <+28>: mov $0x0,%eax
>
> 12 }
> 0x0000555555555160 <+33>: pop %rbp
> 0x0000555555555161 <+34>: ret
> End of assembler dump.
>
> (gdb) n
> 12 }
>
> So far so good, a "next" stepped over the whole of line 11 and stopped at line 12.
>
> Let's confirm where we are now:
>
> (gdb) disassemble /s
> Dump of assembler code for function main:
> reverse.c:
> 10 {
> 0x000055555555513f <+0>: endbr64
> 0x0000555555555143 <+4>: push %rbp
> 0x0000555555555144 <+5>: mov %rsp,%rbp
>
> 11 func1 (); func2 ();
> 0x0000555555555147 <+8>: mov $0x0,%eax
> 0x000055555555514c <+13>: call 0x555555555129 <func1>
> 0x0000555555555151 <+18>: mov $0x0,%eax
> 0x0000555555555156 <+23>: call 0x555555555134 <func2>
> 0x000055555555515b <+28>: mov $0x0,%eax
>
> 12 }
> => 0x0000555555555160 <+33>: pop %rbp
> 0x0000555555555161 <+34>: ret
> End of assembler dump.
>
> Good, we're at the first instruction of line 12.
>
> Now let's undo the "next", with "reverse-next":
>
> (gdb) reverse-next
> 11 func1 (); func2 ();
>
> Seemingly stopped at line 11. Let's see exactly where:
>
> (gdb) disassemble /s
> Dump of assembler code for function main:
> reverse.c:
> 10 {
> 0x000055555555513f <+0>: endbr64
> 0x0000555555555143 <+4>: push %rbp
> 0x0000555555555144 <+5>: mov %rsp,%rbp
>
> 11 func1 (); func2 ();
> 0x0000555555555147 <+8>: mov $0x0,%eax
> 0x000055555555514c <+13>: call 0x555555555129 <func1>
> => 0x0000555555555151 <+18>: mov $0x0,%eax
> 0x0000555555555156 <+23>: call 0x555555555134 <func2>
> 0x000055555555515b <+28>: mov $0x0,%eax
>
> 12 }
> 0x0000555555555160 <+33>: pop %rbp
> 0x0000555555555161 <+34>: ret
> End of assembler dump.
> (gdb)
>
> And lo, we stopped in the middle of line 11! That is a bug, we should have
> stepped back all the way to the beginning of the line. The "reverse-next"
> should have fully undone the prior "next" command.
>
> The above issues were fixed by introducing a new function that looks for
> adjacent PC ranges for the same line, until we notice a line change. Then
> we take that as the start PC of the range. The new start PC for the range
> is used for the control.step_range_start when setting up a step range.
>
> The test case gdb.reverse/map-to-same-line.exp is added to test the fix
> for the issues in scenario 1.
>
> The test case gdb.reverse/func-map-to-same-line.exp was added to test the
> fix for scenario 2 when the binary was compiled with and without line
> table information.
>
> bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28426
>
> Co-authored-by: Luis Machado <luis.machado@arm.com>
> Co-authored-by: Carl Love <cel@us.ibm.com>
> Reviewed-By: Bruno Larsen <blarsen@redhat.com>
> ---
> gdb/infrun.c | 57 +++++++
> gdb/symtab.c | 49 ++++++
> gdb/symtab.h | 16 ++
> .../gdb.reverse/func-map-to-same-line.c | 36 ++++
> .../gdb.reverse/func-map-to-same-line.exp | 140 ++++++++++++++++
> gdb/testsuite/gdb.reverse/map-to-same-line.c | 58 +++++++
> .../gdb.reverse/map-to-same-line.exp | 156 ++++++++++++++++++
> 7 files changed, 512 insertions(+)
> create mode 100644 gdb/testsuite/gdb.reverse/func-map-to-same-line.c
> create mode 100644 gdb/testsuite/gdb.reverse/func-map-to-same-line.exp
> create mode 100644 gdb/testsuite/gdb.reverse/map-to-same-line.c
> create mode 100644 gdb/testsuite/gdb.reverse/map-to-same-line.exp
>
> diff --git a/gdb/infrun.c b/gdb/infrun.c
> index efe2c00c489..31cd817c733 100644
> --- a/gdb/infrun.c
> +++ b/gdb/infrun.c
> @@ -114,6 +114,9 @@ static struct async_event_handler *infrun_async_inferior_event_token;
> Starts off as -1, indicating "never enabled/disabled". */
> static int infrun_is_async = -1;
>
> +static CORE_ADDR update_line_range_start (CORE_ADDR pc,
> + struct execution_control_state *ecs);
> +

This forward-declaration is not needed.

> /* See infrun.h. */
>
> void
> @@ -6769,6 +6772,25 @@ handle_signal_stop (struct execution_control_state *ecs)
> process_event_stop_test (ecs);
> }
>
> +CORE_ADDR
> +update_line_range_start (CORE_ADDR pc, struct execution_control_state *ecs)

Please add a comment for the function.

> +{
> + /* The line table may have multiple entries for the same source code line.
> + Given the PC, check the line table and return the PC that corresponds
> + to the line table entry for the source line that PC is in. */
> + CORE_ADDR start_line_pc = ecs->event_thread->control.step_range_start;
> + gdb::optional<CORE_ADDR> real_range_start;
> +
> + /* Call find_line_range_start to get the smallest address in the
> + linetable for multiple Line X entries in the line table. */
> + real_range_start = find_line_range_start (pc);
> +
> + if (real_range_start.has_value ())
> + start_line_pc = *real_range_start;
> +
> + return start_line_pc;

When I read this, I wonder: why was control.step_range_start not set to
the "real" range start in the first place (not only in the context of
reverse execution, every time it is set)? It would seem more robust
than patching it afterwards in some very specific spots.

I could see some benefits for range-stepping uses cases too (relevant
when debugging remotely). Using your example here:

Line X - [0x0 - 0x8]
Line X - [0x8 - 0x10]
Line X - [0x10 - 0x18]

Imagine we are stopped at 0x14, and we type "next", and 0x14 is a
conditional jump to 0x5. It seems like current GDB would send a "range
step" request to GDBserver, to step in the [0x10, 0x18[ range. When
reaching 0x5, execution would stop, and GDB would resume it again with
the [0x0,0x8[ range. When reaching 0x8, it would stop again, GDB would
resume it with [0x8,0x10[, and so on. If GDB could send a "range step"
request with the [0x0,0x18[ range, it would avoid those unnecessary
intermediary stop.

> +}
> +
> /* Come here when we've got some debug event / signal we can explain
> (IOW, not a random signal), and test whether it should cause a
> stop, or whether we should resume the inferior (transparently).
> @@ -7570,6 +7592,28 @@ process_event_stop_test (struct execution_control_state *ecs)
>
> if (stop_pc_sal.is_stmt)
> {
> + if (execution_direction == EXEC_REVERSE)
> + {
> + /* We are stepping backwards make sure we have reached the
> + beginning of the line. */
> + CORE_ADDR stop_pc = ecs->event_thread->stop_pc ();
> + CORE_ADDR start_line_pc
> + = update_line_range_start (stop_pc, ecs);
> +
> + if (stop_pc != start_line_pc)
> + {
> + /* Have not reached the beginning of the source code line.
> + Set a step range. Execution should stop in any function
> + calls we execute back into before reaching the beginning
> + of the line. */
> + ecs->event_thread->control.step_range_start = start_line_pc;
> + ecs->event_thread->control.step_range_end = stop_pc;
> + set_step_info (ecs->event_thread, frame, stop_pc_sal);
> + keep_going (ecs);
> + return;
> + }
> + }
> +
> /* We are at the start of a statement.
>
> So stop. Note that we don't stop if we step into the middle of a
> @@ -7632,6 +7676,19 @@ process_event_stop_test (struct execution_control_state *ecs)
> set_step_info (ecs->event_thread, frame, stop_pc_sal);
>
> infrun_debug_printf ("keep going");
> +
> + if (execution_direction == EXEC_REVERSE)
> + {
> + CORE_ADDR stop_pc = ecs->event_thread->stop_pc ();
> +
> + /* Make sure the stop_pc is set to the beginning of the line. */
> + if (stop_pc != ecs->event_thread->control.step_range_start)
> + {
> + stop_pc = update_line_range_start (stop_pc, ecs);
> + ecs->event_thread->control.step_range_start = stop_pc;
> + }
> + }
> +
> keep_going (ecs);
> }
>
> diff --git a/gdb/symtab.c b/gdb/symtab.c
> index 27611a34ec4..91d35616eb9 100644
> --- a/gdb/symtab.c
> +++ b/gdb/symtab.c
> @@ -3282,6 +3282,55 @@ find_pc_line (CORE_ADDR pc, int notcurrent)
> return sal;
> }
>
> +/* Compare two symtab_and_line entries. Return true if both have
> + the same line number and the same symtab pointer. That means we
> + are dealing with two entries from the same line and from the same
> + source file.
> +
> + Return false otherwise. */
> +
> +static bool
> +sal_line_symtab_matches_p (const symtab_and_line &sal1,
> + const symtab_and_line &sal2)
> +{
> + return (sal1.line == sal2.line && sal1.symtab == sal2.symtab);

Unnecessary parenthesis.

> +}
> +
> +/* See symtah.h. */
> +
> +gdb::optional<CORE_ADDR>
> +find_line_range_start (CORE_ADDR pc)
> +{
> + struct symtab_and_line current_sal = find_pc_line (pc, 0);
> +
> + if (current_sal.line == 0)
> + return {};
> +
> + struct symtab_and_line prev_sal = find_pc_line (current_sal.pc - 1, 0);
> +
> + /* If the previous entry is for a different line, that means we are already
> + at the entry with the start PC for this line. */
> + if (!sal_line_symtab_matches_p (prev_sal, current_sal))
> + return current_sal.pc;
> +
> + /* Otherwise, keep looking for entries for the same line but with
> + smaller PC's. */
> + bool done = false;
> + CORE_ADDR prev_pc;
> + while (!done)
> + {
> + prev_pc = prev_sal.pc;
> +
> + prev_sal = find_pc_line (prev_pc - 1, 0);
> +
> + /* Did we notice a line change? If so, we are done with the search. */
> + if (!sal_line_symtab_matches_p (prev_sal, current_sal))
> + done = true;
> + }
> +
> + return prev_pc;

Algorithmic complexity question: given that line tables are sorted by
address, would it work to start at the current line table item, and go
look at the previous ones until we find one that is no longer
contiguous and same line? find_pc_line is somewhat heavy, so if we
don't need to do it repeatedly...

> +}
> +
> /* See symtab.h. */
>
> struct symtab *
> diff --git a/gdb/symtab.h b/gdb/symtab.h
> index 404d0ab30a8..f54305636da 100644
> --- a/gdb/symtab.h
> +++ b/gdb/symtab.h
> @@ -2346,6 +2346,22 @@ extern struct symtab_and_line find_pc_line (CORE_ADDR, int);
> extern struct symtab_and_line find_pc_sect_line (CORE_ADDR,
> struct obj_section *, int);
>
> +/* Given PC, and assuming it is part of a range of addresses that is part of a
> + line, go back through the linetable and find the starting PC of that
> + line.
> +
> + For example, suppose we have 3 PC ranges for line X:
> +
> + Line X - [0x0 - 0x8]
> + Line X - [0x8 - 0x10]
> + Line X - [0x10 - 0x18]
> +
> + If we call the function with PC == 0x14, we want to return 0x0, as that is
> + the starting PC of line X, and the ranges are contiguous.

I think that putting this example in the comment is great. It makes it
much more obvious what the function specifically does.

> +*/
> +
> +extern gdb::optional<CORE_ADDR> find_line_range_start (CORE_ADDR pc);
> +
> /* Wrapper around find_pc_line to just return the symtab. */
>
> extern struct symtab *find_pc_line_symtab (CORE_ADDR);
> diff --git a/gdb/testsuite/gdb.reverse/func-map-to-same-line.c b/gdb/testsuite/gdb.reverse/func-map-to-same-line.c
> new file mode 100644
> index 00000000000..da944874e86
> --- /dev/null
> +++ b/gdb/testsuite/gdb.reverse/func-map-to-same-line.c
> @@ -0,0 +1,36 @@
> +/* Copyright 2008-2023 Free Software Foundation, Inc.
> +
> + This program is free software; you can redistribute it and/or modify
> + it under the terms of the GNU General Public License as published by
> + the Free Software Foundation; either version 3 of the License, or
> + (at your option) any later version.
> +
> + This program is distributed in the hope that it will be useful,
> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + GNU General Public License for more details.
> +
> + You should have received a copy of the GNU General Public License
> + along with this program. If not, see <http://www.gnu.org/licenses/>.
> +
> + This test is used to test the reverse-step and reverse-next instruction
> + execution for a source line that contains multiple function calls. */
> +
> +void
> +func1 ()
> +{
> +} /* END FUNC1 */
> +
> +void
> +func2 ()
> +{
> +} /* END FUNC2 */
> +
> +int main ()

int
main (void)

> +{
> + int a, b;
> + a = 1;
> + b = 2;
> + func1 (); func2 ();
> + a = a + b; /* START REVERSE TEST */
> +}
> diff --git a/gdb/testsuite/gdb.reverse/func-map-to-same-line.exp b/gdb/testsuite/gdb.reverse/func-map-to-same-line.exp
> new file mode 100644
> index 00000000000..89e226b0f84
> --- /dev/null
> +++ b/gdb/testsuite/gdb.reverse/func-map-to-same-line.exp
> @@ -0,0 +1,140 @@
> +# Copyright 2008-2023 Free Software Foundation, Inc.
> +
> +# This program is free software; you can redistribute it and/or modify
> +# it under the terms of the GNU General Public License as published by
> +# the Free Software Foundation; either version 3 of the License, or
> +# (at your option) any later version.
> +#
> +# This program is distributed in the hope that it will be useful,
> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> +# GNU General Public License for more details.
> +#
> +# You should have received a copy of the GNU General Public License
> +# along with this program. If not, see <http://www.gnu.org/licenses/>. */
> +
> +# This file is part of the GDB testsuite. It tests reverse stepping.
> +# Lots of code borrowed from "step-test.exp".
> +
> +# This test checks to make sure there is no regression failures for
> +# the reverse-next command when stepping back over two functions in
> +# the same line.
> +
> +require supports_reverse
> +
> +# This test uses the gcc no-column-info command which was added in gcc 7.1.
> +
> +proc run_tests {} {
> + global srcfile
> + global executable
> +
> + runto_main

We typically check for runto_main's success:

if { ![runto_main] } {
return
}

runto_main logs a FAIL on failure. There are a few runto_mains in the
patch.

> + set target_remote [gdb_is_target_remote]

target_remote seems unused

> +
> + with_test_prefix "test1" {
> + gdb_test_no_output "record" "turn on process record"
> + }

with_test_prefix with a single test in it is really just the same as:

gdb_test_no_output "record" "test1: turn on process record"

In fact, you have some other tests with the "test1:" or "test2:" prefix,
I think they should be moved to the with_test_prefix. And maybe use
"next" and "step" instead of "test1" and "test2".

> +
> + # This regression test verifies the reverse-step and reverse-next commands
> + # work properly when executing backwards thru a source line containing
> + # two function calls on the same source line, i.e. func1 (); func2 ();
> + # This test is compiled so the dwarf info not contain the line table
> + # information.
> +
> + # Test 1, reverse-next command
> + # Set breakpoint at the line after the function calls.
> + set bp_start_reverse_test [gdb_get_line_number "START REVERSE TEST" \
> + $srcfile]
> + gdb_breakpoint $srcfile:$bp_start_reverse_test temporary
> +
> + # Continue to break point for reverse-next test.
> + # Command definition: reverse-next [count]
> + # Run backward to the beginning of the previous line executed in the
> + # current (innermost) stack frame. If the line contains function calls,
> + # they will be “un-executed” without stopping. Starting from the first
> + # line of a function, reverse-next will take you back to the caller of
> + # that function, before the function was called, just as the normal next
> + # command would take you from the last line of a function back to its
> + # return to its caller 2 .
> + gdb_continue_to_breakpoint \
> + "test1: stopped at command reverse-next test start location" \
> + ".*$srcfile:$bp_start_reverse_test\r\n.*"
> +
> + # The reverse-next should step all the way back to the beginning of the
> + # line, i.e. at the beginning of the func1 call.
> + gdb_test "reverse-next" ".*func1 \\(\\); func2 \\(\\);.*" \
> + "test1: reverse-next to line with two functions"
> +
> + # We should be stopped at the first instruction of the line. A reverse-step
> + # should step back and stop at the beginning of the previous line b = 2,
> + # i.e. not in func1 ().
> + gdb_test "reverse-stepi" ".*b = 2;.*" \
> + "test1: reverse-stepi to previous line b = 2"
> +
> +
> + # Setup for test 2
> + clean_restart $executable
> + runto_main
> +
> + with_test_prefix "test2" {
> + gdb_test_no_output "record" "turn on process record"
> + }
> +
> + # Test 2, reverse-step command
> + # Set breakpoint at the line after the function calls.
> + gdb_breakpoint $srcfile:$bp_start_reverse_test temporary
> +
> + # Continue to the start of the reverse-step test.
> + # Command definition: reverse-step [count]
> + # Run the program backward until control reaches the start of a
> + # different source line; then stop it, and return control to gdb.
> + # Like the step command, reverse-step will only stop at the beginning
> + # of a source line. It “un-executes” the previously executed source
> + # line. If the previous source line included calls to debuggable
> + # functions, reverse-step will step (backward) into the called function,
> + # stopping at the beginning of the last statement in the called
> + # function (typically a return statement). Also, as with the step
> + # command, if non-debuggable functions are called, reverse-step will
> + # run thru them backward without stopping.
> +
> + gdb_continue_to_breakpoint \
> + "test2: stopped at command reverse-step test start location" \
> + ".*$srcfile:$bp_start_reverse_test\r\n.*"
> +
> + # The first reverse step should take us call of func2 ().
> + gdb_test "reverse-step" ".*END FUNC2.*" \
> + "test2: reverse-step into func2 "
> +
> + # The second reverse step should take us into func1 ().
> + gdb_test "reverse-step" ".*END FUNC1.*" \
> + "test2: reverse-step into func1 "
> +
> + # The third reverse step should take us call of func1 ().
> + gdb_test "reverse-step" ".*func1 \\(\\); func2 \\(\\);.*" \
> + "test2: reverse-step to line func1(); func2(), at call for func1 "
> +
> + # We should be stopped at the first instruction of the line. A reverse
> + # stepi should take us to b = 2 ().
> + gdb_test "reverse-stepi" ".*b = 2;.*" \
> + "test2: reverse-stepi to line b = 2 "
> +}
> +
> +set srcfile func-map-to-same-line.c
> +set executable func-map-to-same-line

Wondering if this test should use standard_testfile (like almost every
other tests) to set these.

> +
> +# test with and without gcc column info enabled
> +foreach_with_prefix with_column_info {yes no} {
> + if {$with_column_info == "yes"} {
> + set options [list debug column-info]
> + } else {
> + set options [list debug no-column-info]
> + }

I didn't think of this when proposing the foreach_with_prefix, but you
could perhaps use:

foreach_with_prefix column_info_flag {column-info no-column-info}

... to avoid this boilerplate. You can then use $column_info_flag
directly when setting options.

> +
> + if {[build_executable "failed to prepare" $executable $srcfile \
> + $options] == -1} {
> + return -1
> + }
> +
> + clean_restart $executable

clean_restart can go in run_tests.

> + run_tests
> +}
> diff --git a/gdb/testsuite/gdb.reverse/map-to-same-line.c b/gdb/testsuite/gdb.reverse/map-to-same-line.c
> new file mode 100644
> index 00000000000..f20d778f40e
> --- /dev/null
> +++ b/gdb/testsuite/gdb.reverse/map-to-same-line.c
> @@ -0,0 +1,58 @@
> +/* Copyright 2008-2023 Free Software Foundation, Inc.

Just wondering if the copyright years are right.

> +
> + This program is free software; you can redistribute it and/or modify
> + it under the terms of the GNU General Public License as published by
> + the Free Software Foundation; either version 3 of the License, or
> + (at your option) any later version.
> +
> + This program is distributed in the hope that it will be useful,
> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + GNU General Public License for more details.
> +
> + You should have received a copy of the GNU General Public License
> + along with this program. If not, see <http://www.gnu.org/licenses/ >. */
> +
> +/* The purpose of this test is to create a DWARF line table that contains two
> + or more entries for the same line. When stepping (forwards or backwards),
> + GDB should step over the entire line and not just a particular entry in the
> + line table. */
> +
> +int
> +main ()

void in the parenthesis

> +{ /* TAG: main prologue */
> + asm ("main_label: .globl main_label");
> + int i = 1, j = 2, k;
> + float f1 = 2.0, f2 = 4.1, f3;
> + const char *str_1 = "foo", *str_2 = "bar", *str_3;
> +
> + asm ("line1: .globl line1");
> + k = i; f3 = f1; str_3 = str_1; /* TAG: line 1 */
> +
> + asm ("line2: .globl line2");
> + k = j; f3 = f2; str_3 = str_2; /* TAG: line 2 */
> +
> + asm ("line3: .globl line3");
> + k = i; f3 = f1; str_3 = str_1; /* TAG: line 3 */
> +
> + asm ("line4: .globl line4");
> + k = j; f3 = f2; str_3 = str_2; /* TAG: line 4 */
> +
> + asm ("line5: .globl line5");
> + k = i; f3 = f1; str_3 = str_1; /* TAG: line 5 */
> +
> + asm ("line6: .globl line6");
> + k = j; f3 = f2; str_3 = str_2; /* TAG: line 6 */
> +
> + asm ("line7: .globl line7");
> + k = i; f3 = f1; str_3 = str_1; /* TAG: line 7 */
> +
> + asm ("line8: .globl line8");
> + k = j; f3 = f2; str_3 = str_2; /* TAG: line 8 */
> +
> + asm ("main_return: .globl main_return");
> + k = j; f3 = f2; str_3 = str_2; /* TAG: main return */
> +
> + asm ("end_of_sequence: .globl end_of_sequence");
> + return 0; /* TAG: main return */
> +}
> diff --git a/gdb/testsuite/gdb.reverse/map-to-same-line.exp b/gdb/testsuite/gdb.reverse/map-to-same-line.exp
> new file mode 100644
> index 00000000000..16a359d90ec
> --- /dev/null
> +++ b/gdb/testsuite/gdb.reverse/map-to-same-line.exp
> @@ -0,0 +1,156 @@
> +# Copyright 2008-2023 Free Software Foundation, Inc.
> +
> +# This program is free software; you can redistribute it and/or modify
> +# it under the terms of the GNU General Public License as published by
> +# the Free Software Foundation; either version 3 of the License, or
> +# (at your option) any later version.
> +#
> +# This program is distributed in the hope that it will be useful,
> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> +# GNU General Public License for more details.
> +#
> +# You should have received a copy of the GNU General Public License
> +# along with this program. If not, see <http://www.gnu.org/licenses/ >.
> +
> +# When stepping (forwards or backwards), GDB should step over the entire line
> +# and not just a particular entry in the line table. This test was added to
> +# verify the find_line_range_start function properly sets the step range for a
> +# line that consists of multiple statements, i.e. multiple entries in the line
> +# table. This test creates a DWARF line table that contains two entries for
> +# the same line to do the needed testing.
> +
> +# This test can only be run on targets which support DWARF-2 and use gas.
> +load_lib dwarf.exp
> +require dwarf2_support
> +
> +# The DWARF assembler requires the gcc compiler.
> +require is_c_compiler_gcc
> +
> +# This test suitable only for process that can do reverse execution
> +require supports_reverse
> +
> +standard_testfile .c .S
> +
> +if { [prepare_for_testing "failed to prepare" ${testfile} ${srcfile}] } {
> + return -1
> +}
> +
> +set asm_file [standard_output_file $srcfile2]
> +Dwarf::assemble $asm_file {
> + global srcdir subdir srcfile
> + declare_labels integer_label L
> +
> + # Find start address and length of program
> + lassign [function_range main [list ${srcdir}/${subdir}/$srcfile]] \
> + main_start main_len
> + set main_end "$main_start + $main_len"
> +
> + cu {} {
> + compile_unit {
> + {language @DW_LANG_C}
> + {name map-to-same-line.c}
> + {stmt_list $L DW_FORM_sec_offset}
> + {low_pc 0 addr}
> + } {
> + subprogram {
> + {external 1 flag}
> + {name main}
> + {low_pc $main_start addr}
> + {high_pc $main_len DW_FORM_data4}
> + }
> + }
> + }
> +
> + lines {version 2 default_is_stmt 1} L {
> + include_dir "${srcdir}/${subdir}"
> + file_name "$srcfile" 1
> +
> + # Generate the line table program with distinct source lines being
> + # mapped to the same line entry. Line 1, 5 and 8 contain 1 statement
> + # each. Line 2 contains 2 statements. Line 3 contains 3 statements.
> + program {
> + DW_LNE_set_address $main_start
> + line [gdb_get_line_number "TAG: main prologue"]
> + DW_LNS_copy
> + DW_LNE_set_address line1
> + line [gdb_get_line_number "TAG: line 1" ]
> + DW_LNS_copy
> + DW_LNE_set_address line2
> + line [gdb_get_line_number "TAG: line 2" ]
> + DW_LNS_copy
> + DW_LNE_set_address line3
> + line [gdb_get_line_number "TAG: line 2" ]
> + DW_LNS_copy
> + DW_LNE_set_address line4
> + line [gdb_get_line_number "TAG: line 3" ]
> + DW_LNS_copy
> + DW_LNE_set_address line5
> + line [gdb_get_line_number "TAG: line 3" ]
> + DW_LNS_copy
> + DW_LNE_set_address line6
> + line [gdb_get_line_number "TAG: line 3" ]
> + DW_LNS_copy
> + DW_LNE_set_address line7
> + line [gdb_get_line_number "TAG: line 5" ]
> + DW_LNS_copy
> + DW_LNE_set_address line8
> + line [gdb_get_line_number "TAG: line 8" ]
> + DW_LNS_copy
> + DW_LNE_set_address main_return
> + line [gdb_get_line_number "TAG: main return"]
> + DW_LNS_copy
> + DW_LNE_set_address end_of_sequence
> + DW_LNE_end_sequence
> + }
> + }
> +}
> +
> +if { [prepare_for_testing "failed to prepare" ${testfile} \
> + [list $srcfile $asm_file] {nodebug} ] } {
> + return -1
> +}
> +
> +runto_main
> +
> +# Print the line table
> +gdb_test_multiple "maint info line-table ${testfile}" "" {
> + -re "\r\n$decimal\[ \t\]+$decimal\[ \t\]+($hex)\[ \t\]+Y\[^\r\n\]*" {
> + lappend is_stmt $expect_out(1,string)
> + exp_continue
> + }
> + -re -wrap "" {
> + }
> +}
> +
> +# Do the reverse-step test
> +gdb_test_no_output "record" "turn on process record"
> +
> +set bp_main_return [gdb_get_line_number "TAG: main return" $srcfile]
> +gdb_breakpoint $srcfile:$bp_main_return
> +gdb_continue_to_breakpoint "run to end of main, reverse-step test" ".*$srcfile:$bp_main_return.*"
> +gdb_test "display \$pc" ".*pc =.*" "display pc, reverse-step test"
> +
> +# At this point, GDB has already recorded the execution up until the return
> +# statement. Reverse-step and test if GDB transitions between lines in the
> +# expected order. It should reverse-step across lines 8, 5, 3, 2 and 1.
> +foreach line {8 5 3 2 1} {
> + gdb_test "reverse-step" ".*TAG: line $line.*" "reverse step to line $line"
> +}
> +
> +## Clean restart, test reverse-next command
> +clean_restart ${testfile}
> +runto_main
> +gdb_test_no_output "record" "turn on process record, reverst-next test"
> +
> +set bp_main_return [gdb_get_line_number "TAG: main return" $srcfile]
> +gdb_breakpoint $srcfile:$bp_main_return
> +gdb_continue_to_breakpoint "run to end of main, reverse-next test" ".*$srcfile:$bp_main_return.*"
> +gdb_test "display \$pc" ".*pc =.*" "display pc, reverse-next test"
> +
> +# At this point, GDB has already recorded the execution up until the return
> +# statement. Reverse-next and test if GDB transitions between lines in the
> +# expected order. It should reverse-next across lines 8, 5, 3, 2 and 1.
> +foreach line {8 5 3 2 1} {
> + gdb_test "reverse-next" ".*TAG: line $line.*" "reverse next to line $line"
> +}

It seems like the step and next tests are identical, so I guess it could
be factored out using:

foreach_with_prefix method {step next} {
...
}

?

Simon